1. Field of the Invention
The present invention relates to a video camera and a video camera system. More particularly, the invention relates to a video camera and a video camera system capable of reducing color differences between the innovative video cameras that make up the system by adjusting their gains and DC offset values in keeping with the red, green and blue signals obtained through imaging operation.
2. Description of the Related Art
FIG. 9 is a schematic view outlining the constitution of a conventional video camera. In FIG. 9, a light source 1 illuminates an object 2. The light coming from the object 2 through an imaging lens 3 enters an optical filter 4 such as a CC (color conversion) filter or ND (neutral density) filter, and an IR (infrared) cut filter 5. Past the filter, the incident light is fed to a color separation prism 6 for separation into red, green and blue light components which are led to CCD solid state image sensing devices 7R, 7G and 7B respectively. On the imaging planes of the image sensing devices 7R, 7G and 7B, the red, green and blue images of the object 2 are focused for imaging. The image sensing devices 7R, 7G and 7B output signals that are amplified by amplifiers 8R, 8G and 8B respectively. The outputs from the amplifiers provide red, green and blue signals R, G and B as tristimulus values.
FIG. 10A shows a typical spectral distribution characteristic I(xcex) of the camera input integrating the reflectance ratio of the illuminated object 2 and other relevant factors. FIG. 10B graphically illustrates typical spectral distribution characteristics r(xcex), g(xcex) and b(xcex) integrating the properties of the optical filter 4, IR cut filter 5, color separation prism 6, and imaging devices 7R, 7G and 7B. If the gains of the amplifiers 8R, 8G and 8B are represented by Ar, Ag and Ab, the tristimulus values R, G and B are given by the following equations (1):
R=Ar∫I(xcex)r(xcex)dxcex
G=Ag∫I(xcex)g(xcex)dxcex
B=Ab∫I(xcex)b(xcex)dxcexxe2x80x83xe2x80x83(1)
Suppose that a plurality of video cameras constitute a video camera system. In this system, each of the tristimulus values R, G and B needs to be the same between the component video cameras so that the system may absorb color differences between the cameras for color matching.
Consider a case where two video cameras take pictures of the same object. For this setup, it is assumed that the spectral distribution of one of the video cameras is represented by r1(xcex), g1(xcex) and b1(xcex), and that of the other video camera by r2(xcex), g2(xcex) and b2(xcex). It is also assumed that the gains of the amplifiers 7R, 7G and 7B in one video camera are designated by Ar1, Ag1, and Ab1, respectively, and those of the corresponding amplifiers in the other video camera by Ar2, Ag2 and Ab2 respectively. In that case, the tristimulus values R1, G1 and B1 of one video camera are given by the equations (2) below, and the tristimulus values R2, G2 and B2 Of the other video camera are expressed by the following equations (3):
R1=Ar1∫I(xcex)r1(xcex)dxcex
G1=Ag1∫I(xcex)g1(xcex)dxcex
B1=Ab1∫I(xcex)b1(xcex)dxcexxe2x80x83xe2x80x83(2)
R2=Ar2∫I(xcex)r2(xcex)dxcex
G2=Ag2∫I(xcex)g2(xcex)dxcex
B2=Ab2∫I(xcex)b2(xcex)dxcexxe2x80x83xe2x80x83(3)
To make the tristimulus values R1, G1 and B1 of one video camera match the corresponding tristimulus values R2, G2 and B2 Of the other video camera for color matching requires using at least three variables. In one example, the levels of the tristimulus values R2, G2 and B2 would be adjusted by use of six variables, i.e., gains Gr, Gg and Gb, and DC offset values Or, Og and Ob in the equations (4) below. The adjustments would provide tristimulus values R2xe2x80x2, G2xe2x80x2 and B2xe2x80x2 matching the tristimulus values R1, G1 and B1.
Rxe2x80x22=GrR2+Or
Gxe2x80x22=GgG2+Og
Bxe2x80x22=GbB2+Obxe2x80x83xe2x80x83(4)
However, one disadvantage of conventional video cameras is that their gains and DC offset values (black level) are fixed. This makes it impossible to match the tristimulus values of a plurality video cameras constituting a video camera system; color differences between different video cameras within a system cannot be absorbed thereby for color matching.
It is therefore an object of the present invention to provide a video camera and a video camera system capable of absorbing the color differences between a plurality of such video cameras making up the system in order to ensure appropriate color matching between the component cameras.
In carrying out the invention and according to one aspect thereof, there is provided a video camera comprising: level detecting means for detecting the levels of a red, a green and a blue signal obtained through imaging operation; and color matching means for adjusting the gains and/or the DC current offset values of the red, green and blue signals in accordance with those levels of the red, green and blue signals which are detected by the level detecting means.
According to another aspect of the invention, there is provided a video camera system comprising a plurality of video cameras and a controller. Each of the plurality of video cameras includes level detecting means for detecting the levels of a red, a green and a blue signal obtained through imaging operation; and color matching means for adjusting the gains and/or the DC current offset values of the red, green and blue signals. The controller controls the operation of the color matching means of the plurality of video cameras in accordance with those levels of the red, green and blue signals which are detected by the level detecting means.
The color matching means of each video camera adjusts the gains and/or DC offset values of the red, green and blue signals. Where a plurality of video cameras making up a video camera system acquire their respective red, green and blue signals through imaging operation, the gains and/or DC offset values of these red, green and blue signals are adjusted in accordance with the levels of the signals, whereby the color differences between the component video cameras within the system are absorbed.
Other objects, features and advantages of the present invention will become apparent in the following specification and accompanying drawings.